The following video shows one of the best presentations I've happen to see describing one of the most significant changes we are living today.
This is a short description from blip.tv:
This session examines the concept of cloud computing, its benefits and risks and why it matters. We then explore the difference between private and public clouds and the importance of open source in this field. Finally we take a look at the future of this industry and use all these concepts to explain “why cloud vendors lie to you and how they steal your money.”